This invention relates to a compressor or turbine adjustable blade assembly which is easily fabricated and which exhibits excellent damping characteristics.
Blades utilized in most turbines and compressors are subjected to high stresses at or near the resonant blade frequency. These stresses induce fatigue fractures within the blade which lead to blade failure. Failure can occur over a relatively long period of time or, under certain operating conditions, in a matter of seconds.
Most blades heretofore have been constructed of a single piece of material which includes both the airfoil and the blade support structure. In general, the contour of the airfoil is generally thinner and relatively wider than that of the root or supporting structure and, as a consequence, a good deal of machining is required to fabricate the blade from a blank. A good deal of waste material is thus generated and the extensive machining required has proven to be costly. Furthermore, hand-contouring of the blade after finished machining is not uncommon. Both the profile of the airfoil and the outer surface of the blade platform are generally complex shapes which, when brought together, describe a geometry that cannot be generated by conventional machine tools. To insure that an unimpeded flow passage is maintained about the blade, the region where the airfoil joins the platform is ordinarily hand-filed to a smooth contour.